Abstract Background Mycobacterium avium complex (MAC), including Mycobacterium intracellulare is a member of slow-growing mycobacteria and contributes to a substantial proportion of nontuberculous mycobacterial lung disease in humans affecting immunocompromised and elderly populations. Adaptation of pathogens in hostile environments is crucial in establishing infection and persistence within the host. However, the sophisticated cellular and molecular mechanisms of stress response in M. intracellulare still need to be fully explored. We aimed to elucidate the transcriptional response of M. intracellulare under acidic and oxidative stress conditions. Results At the transcriptome level, 80 genes were shown [FC] ≥ 2.0 and p < 0.05 under oxidative stress with 10 mM hydrogen peroxide. Specifically, 77 genes were upregulated, while 3 genes were downregulated. In functional analysis, oxidative stress conditions activate DNA replication, nucleotide excision repair, mismatch repair, homologous recombination, and tuberculosis pathways. Additionally, our results demonstrate that DNA replication and repair system genes, such as dnaB, dinG, urvB, uvrD2, and recA, are indispensable for resistance to oxidative stress. On the contrary, 878 genes were shown [FC] ≥ 2.0 and p < 0.05 under acidic stress with pH 4.5. Among these genes, 339 were upregulated, while 539 were downregulated. Functional analysis highlighted nitrogen and sulfur metabolism pathways as the primary responses to acidic stress. Our findings provide evidence of the critical role played by nitrogen and sulfur metabolism genes in the response to acidic stress, including narGHIJ, nirBD, narU, narK3, cysND, cysC, cysH, ferredoxin 1 and 2, and formate dehydrogenase. Conclusion Our results suggest the activation of several pathways potentially critical for the survival of M. intracellulare under a hostile microenvironment within the host. This study indicates the importance of stress responses in M. intracellulare infection and identifies promising therapeutic targets.

Helicobacter pylori (H. pylori) was defined as a Class 1 pathogenic carcinogen by WHO causing chronic inflammation in the stomach, thereby increasing the risk of gastric cancer. Various virulence factors are involved in the mechanism of gastric cancer caused by H. pylori infection. These virulence factors usually show different expression levels depending on the environment of H. pylori, which can affect the risk of gastric cancer. In this study, the differences in the expression levels of major virulence factors of H. pylori depending on the environment were investigated by comparing expression levels of H. pylori cultured with AGS or alone. As a result, there was no difference in the expression of adhesins of alpA, sabA, and babA even after co-culture with AGS cells. In addition, the co-culture environment did not induce a difference in the expression levels of flaA and ureB. On the other hand, H. pylori co-cultured with AGS cells showed low expression levels of cagA, groEL, and oipA and high expression of vacA compared to H. pylori cultured alone. Our results suggest that not only the presence or absence of virulence factor genes but also differences in expression levels should be considered when evaluating the risk of gastric cancer after H. pylori infection based on the virulence factors.

In this study, frosting experiment was conducted to investigate the characteristics of frost formed on heat exchanger fins of non-uniform temperature distribution. Temperature distribution and frost characteristics of a 2-D fin surface were investigated in the airflow direction and the direction perpendicular to airflow. Temperature gradient was very small in the airflow direction, while it was large in the direction perpendicular to airflow due to fin heat conduction. The variations of the frost thickness gradient and the frost density gradient in the direction perpendicular to airflow were significant. On the other hand, the temperature gradient on frost surface in the direction perpendicular to airflow was significant at the early stage of frosting, while it decreased gradually as time elapsed.